This invention relates to a microvibration detector using a single piezoelectric element as both sensor and alarm generator. More particularly, this invention relates to a microvibration detection and alarm device of a simple circuit configuration wherein a sound emitter using a single element having a piezoelectric effect serves concurrently as a vibration detector and a sound emitter.
A number of types of sensors designed to detect vibration of various kinds including sound and dynamic pressure and to trigger a warning or the like have been proposed to date. In sensors which detect vibrations electrically, the introduction of piezoelectric elements has led to improved sensitivity and performance and reduced sensor size. These sensors utilize, as their input, the electromotive force which is generated by a piezoelectric element when it is subjected to vibration. Although alarm devices employing such sensors are available in various designs, all operate on the same basic principle. An electric signal from the piezoelectric element is amplified and the resultant amplified signal is utilized to actuate a sound emitter such as a speaker or a buzzer.
Increased sensitivity, reduced size, and lower power consumption have been realized by using piezoelectric elements at both the input and output stages of the sensors. As is plain from the foregoing description, however, the alarms of this type require an amplifier, an oscillator, and a sound emitter in addition to a vibration sensor. Further miniaturization of these alarms by the use of smaller and simpler circuits has proved difficult. Efforts to attain the desired reduction in size, cost and power consumption by omitting circuit parts sensor, or even sound emitters have proved impracticable.